1. Field of the Invention
The present invention relates to a temperature control device for a catalyst, which controls the temperature of a catalyst which purifies exhaust gases discharged from an internal combustion engine.
2. Description of the Related Art
Conventionally, as a temperature control device of this kind, one disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2000-320386 is known. In this temperature control device, when a catalyst is not in an activated state, fuel is supplied to an internal combustion engine in three divided times, whereby the temperature of exhaust gases is raised, which causes the temperature of the catalyst to be raised. The amount of fuel supplied in a single time is set to ⅓ of the total amount of fuel supply, and this total amount of fuel supply is calculated by adding a predetermined correction term to a base value of the amount of fuel supply calculated according to the rotational speed of the engine and a demanded torque. Further, the timing of fuel supply is set such that a time interval between the first-time supply and the second-time supply, and a time interval between the second-time supply and the third-time supply are respective fixed time intervals equal to each other. On the other hand, when the catalyst is in the activated state, one-time supply of fuel to the engine is performed. The amount of fuel for the one-time supply is calculated according to the engine speed and the demanded torque.
It is effective in promoting the activation of the catalyst and promptly ensuring the purification ability of the catalyst to increase the amount of fuel supply when the catalyst is not in the activated state as in the above-mentioned conventional temperature control device. However, if such combustion is performed as will make higher the temperature of exhaust gases, unburned fuel contained in the exhaust gases increases. Further, even if the temperature of exhaust gases is rapidly raised, the temperature of the catalyst does not immediately follow this. On the other hand, in the conventional temperature control device, when the catalyst is not in the activated state, the amount of fuel supply is merely calculated according to the engine speed and the demanded torque to raise the temperature of exhaust gases, irrespective of the temperature of the catalyst. Therefore, there is a case where high-temperature exhaust gases containing a lot of unburned fuel are supplied to the catalyst which is not sufficiently activated, and in this case, there is a fear that the unburned fuel is emitted into the air without being completely purified, resulting in an increase in exhaust emissions.
Further, in the conventional temperature control device, the fuel supply is performed at fixed equal intervals, the entire combustion time period over which combustion is performed in one combustion cycle is substantially fixed. For this reason, if the combustion time period is short, it is difficult for the temperature of exhaust gases to be raised, whereby it is impossible to rapidly raise the temperature of the catalyst and hence it is impossible to rapidly activate the catalyst, which increases exhaust emissions. Inversely, if the combustion time period is long, the temperature of exhaust gases becomes too high, which also increases exhaust emissions.
Further, if the temperature of the catalyst is too high, the ability of the catalyst for purifying exhaust gases by the catalyst tends to be lowered. On the other hand, in the conventional temperature control device, when the catalyst is in the activated state, the amount of fuel supply is calculated according to the engine speed and the demanded torque, irrespective of the temperature of the catalyst. Therefore, there is a case where as the temperature of exhaust gases becomes higher, the temperature of the catalyst becomes too high, and in this case, there is a fear that the exhaust gases are emitted into the air without being sufficiently purified due to degradation of the purification ability of the catalyst, which increases exhaust emissions.